1 files changed, 31 insertions, 0 deletions
diff --git a/gfx/skia/skia/src/utils/SkMatrix22.h b/gfx/skia/skia/src/utils/SkMatrix22.h
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index 0000000000..c8bcd5f6bd
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+++ b/gfx/skia/skia/src/utils/SkMatrix22.h
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkMatrix22_DEFINED
+#define SkMatrix22_DEFINED
+
+#include "include/core/SkPoint.h"
+
+class SkMatrix;
+
+/** Find the Givens matrix G, which is the rotational matrix
+ *  that rotates the vector h to the positive hoizontal axis.
+ *  G * h = [hypot(h), 0]
+ *
+ *  This is equivalent to
+ *
+ *  SkScalar r = h.length();
+ *  SkScalar r_inv = r ? SkScalarInvert(r) : 0;
+ *  h.scale(r_inv);
+ *  G->setSinCos(-h.fY, h.fX);
+ *
+ *  but has better numerical stability by using (partial) hypot,
+ *  and saves a multiply by not computing r.
+ */
+void SkComputeGivensRotation(const SkVector& h, SkMatrix* G);
+
+#endif